Animals having a developed rumen function utilize the feed which is consumed by first degrading the carbohydrate (the main nutritive portion) to pyruvate. The pyruvate is further metabolized to volatile fatty acid (VFA) derivatives, which include acetate, propionate and butyrate. The animals are capable of producing propionate in the rumen and of absorbing propionate from the gut more efficiently than either acetate or butyrate. One method for improving the efficiency of feed utilization by ruminants therefore involves altering the rumen function to increase propionate production at the expense of acetate and butyrate production.
Another method for improving efficiency involves inhibition of methane production. Methane gas is a product of metabolization in the rumen, and is generally lost through eructation. This represents an energy loss which can be minimized by inhibiting methane formation.
It has now been discovered that certain phthalides are effective in increasing propionate production in animals having a developed rumen function, and also inhibit methane production. The compounds therefore are valuable in improving the efficiency of feed utilization by ruminants.
Phthalides are well known in the art. Several 3-(trichloromethyl)phthalides were synthesized by Fritsch, Ann., 296, 344; Beilstein, 18, 20. A number of 6-hydroxy(and 6-alkoxy)-3-(trichloromethyl)phthalide derivatives have been reported; see Chem. Abs., 61, 11927H et. seq. and 63, 14746E et. seq. Phthalides have been employed in the treatment of plant fungal diseases such as rice blast (Japanese No. 7131350), and as pesticides and pharmaceuticals, (see U.S. Pat. No. 3,342,837). Phthalides have not heretofore been employed in ruminants for improving feed utilization efficiency.